1. Field of the Invention
The present invention relates to a data receiving apparatus, a data transmitting and receiving apparatus, and a data transmission system using the same which are used for transmitting a plurality of transmission packets on the same transmission path.
2. Description of the Related Art
As a system for transmitting a digital video signal (hereinafter, simply described as a video signal) etc. among apparatuses used for the editing of the video image etc., a serial digital interface (SDI) system has been conventionally used. The signal format of the SDI system is defined in SMPTE-295M of the SMPTE (Society of Motion Picture and Television Engineering) as the standard of a video signal and audio signal of the digital format.
The SDI system is used for the transmission of a video signal of the digital format of the D1 system and D2 system and the transmission speed thereof is as high as 270 MHz.
However, in the SDI system, the amount of signals which can be transmitted is restricted to only one channel's worth of the video signal and only eight channels' worth of audio signals of the base band, so it is not always flexible enough to meet the demands for multi-media or multi-channel systems which are now arising in the field of broadcasting or editing of video images.
For this reason, an SDDI system having a higher flexibility to multi-media systems wherein for example variable length video signal data can be transmitted while having a considerably high interchangeability with the SDI system has been proposed.
To transmit a signal of the SDI system and a signal of the SDDI system, use of a data transmitting apparatus 8 shown in FIG. 1 can be considered.
The data transmitting apparatus 8 is constituted by a data transmitting device 800 and a data receiving device 830. The data transmitting device 800 is constituted so as to convert an input signal of the SDI system (SDI data) and data of the SDDI system (SDDI data) to serial data by the FIFos 812 and 822 and parallel to serial conversion circuits (P/S conversion circuits) 810 and 820 and transmit the serial data to the data receiving device 830 using different transmission paths.
Also, the data receiving device 830 is constituted so as to separate these signals transmitted through different transmission paths from the data transmitting device 800 to the original SDI data and SDDI data by the serial to parallel conversion circuits (S/P conversion circuits) 842 and 852 and the FIFOs 840 and 850 and output the converted data to the outside.
Note that, a synchronization signal defining the timing of signal transmission etc. between the data transmitting device 800 and the data receiving device 830 is transmitted from the data receiving device 830 side to the data transmitting device 800 side by using still another transmission path by the FIFO 832 and P/S conversion circuit 834. The data transmitting device 800 reproduces the original synchronization signal by the S/P conversion circuit 802 and the FIFO 804 and uses the same for internal processing etc.
Here, for the reason that the number of the transmission paths should be decreased, that the work for laying the transmission paths should be simplified, etc., there is a demand that the signal of the SDI system and the signal of the SDDI system be transmitted by using the same transmission path. However, in contrast to the fact that only fixed length data are contained in a signal of the SDI system, other than the fixed length data, variable length data is sometimes contained in a signal of the SDDI system. Accordingly, where these signals are transmitted by using the same transmission path, it is necessary to separate the signal of the SDI system and the signal of the SDDI system on the reception side and supply the same to the video editing devices etc. corresponding to the signals of the systems.